Diffusion coated articles



April 12, 1955 R. B. BARNES DIFFUSION COATED ARTICLES "A. /2/ M- 1'19 5% fly. l

Filed July 15, 1950 2 Shets-Sheet 1 w mzzw $2 INVENTOR ROBERT BOWLING BARNES BY ATTOR NEY a April 12, 1955 R. s. BARNES 2,705,262

DIFFUSION COATED ARTICLES Filed July 15, 1950 2 Sheets-Sheet 2 INVENTOR ROBERT BOWLING BARNES ATTORNEY 2,705,262 Patented Apr. 12, l$55 p IQQ DIFU3N EGATED ARTIQLES Robert Bowling Barnes, Stamford, Conn., assignor to American Gptical Company, Southbridge, Mass, a voluntary association of lliassachusetts Application July 15, 1950, Serial No. 173,993

9 Claims. (C 3l.3--2) This invention relates to novel means and method of eliminating specular reflection from the reflective surface of an article and relates particularly to the provision of a novel coating and method of making and applying the same, and to a novel article resulting therefrom. I

One of the principal objects of the invention is to provide a composition in the form of a liquid suspension which may be applied to the reflective s urrace of an article to produce a coating which will eliminate specular reflection and novel method of making and applying the same.

Another object is to provide a coating of the above character and method of applying the same whereby specular reflection from the reflecting surface of an article having the coating thereon will be so ditfused that no isolated bright spots will be visible and with the resultant coated surface further having the appearance of being smooth and substantially uniform in texture.

Another object is to provide a composition compr sing a transparent liquid bonding agent havin substantially uniformly dispersed therein a plurality of small nearly spherical transparent material which when placed upon the rellectin surface of an article as by painting, spraying, clipping or other suitable method and when the liquid is dry and hard or becomes polymerized, the surface will have a texture simulating a multitude of small contiguously related spherical elements with pa rt1a lly filled depressions therebetween whereby light impinging thereon and which would normally produce specular reflection will be diffused and the image formation destroyed.

Another object is to provide a coating of the above nature with ultra-violet absorbing characteristics.

Another object is to provide a coating of this nature having desired visible light-absorbing characteristics.

Another object is to provide a composition and a coating resulting therefrom which embodies a liquid having suspended therein relatively small transparent nearly spherical particles wherein the related indrces of refraction of said liquid and particles is controlled accord ing to the end results desired.

Another object is to provide an article having a d ffusing coating formed thereon in accordance with the above and further having a reflection-reduction coating on said diffusing coating.

Other objects and advantages of the invention will become apparent from the following description taken in connection with the accompanying drawings and it will be apparent that many changes may be made in the details of construction, arrangement of parts and steps of the method shown and described without departing from the spirit of the invention as expressed in the accompanying claims. I, therefore, do not wish to be limited to the exact details of construction, arrangement of parts and steps of the method shown and described as the preferred forms only are given by way of illustration.

Referring to the drawings:

Fig. l is a fragmentary view of an article having a coating thereon and diagrammatically illustrating the effect of said coating on light'rays impinging thereon;

Fig la is a view generally similar to Fig. l diagrammatically illustrating reflected light from a non-coated surface; t p

Fig. 2 is a view generally similar to Fig. 1 illustrating multiple layers instead of a single layer;

Fig. 3 is an enlarged fragmentary view generally similar to Fig. 1 having a portion thereof provided with a non-reflection coating;

Fig. 4 is a View generally similar to Fig. 1 illustrating a further feature of the invention when a light-absorbing dye1 is placed in the solution of the coating composition; an

Fig. 5 is a view generally similar to Fig. 4 diagrammatically illustrating another feature of the invention.

Referring more particularly to the drawings wherein like characters of reference designate lilac parts throughout the several views, the article 4, which in the present instance, is described as being the face of a television tube, is formed of a transparent material such as glass having an outer reflecting surface 5 and an inner phosphor coating 6 thereon.

Under normal conditions of use, light rays from an exterior source of light 7, as illustrated in Fig. 1a, impinging on the surface 5 would normally be specularly reflected, as illustrated by the lines 8, and when received by the eye 9 of an observer would produce a distinct image of the source '7 as being located at '7.

In following the teachings of the present invention, a composition which embodies a liquid binder it) having a plurality of relatively small transparent nearly spherical particles or beads 11 therein is applied to the surface 5 as by spraying, painting, dipping or other suitable means, see Figures 1 and 3 to 5 Tie size of the individual particles or heads is controlled according to the distance at which the picture is to be viewed. For example, if the picture is to be viewed close to, the size of the particles should be reduced proporti nately. If, on the other hand, the picture is to be constantly viewed at a considerable distance, then the particles can be proportionately greater in size, keeping in mind that the size of particles is preferably so controlled that no particle is individually visible at the distance of vie 'ing and so that the resultant coated surface has the appearance of being smooth and substantially uniform in texture. it has been found that if the size of the individual particles or beads are such that they are not readily visible at a distance of approximately ten inches very efficient and practical results will be obtained. in practice, particles of from 3 to 5 microns in size have been found to be very eilicient as they do not readily settle in the suspension and may be easily and relatively uniform applied. If they are too coarse, they settle too quickly and may result in a surface having some of said particles individually visible.

Although particles of from 3 to 5' microns in size have been found to be. very efdcient, the said size ofparticles may be from less than 16 3 microns or of a millimeter, as their upper limit, and which is at the limit of visibility at 1!) inches, and must be in the order of magnitude of more than a wave length of light as the lower limit in size, to if they are too small they do not perform the desired function.

In forming the composition, any suitable transparent liquid binder in which the transparent nearly spherical particles or beads may be suspended may be used; This, of course, depends upon the nature of the beads and the binder must be such as not to act as a solvent for said beads.

For example, the liquid suspension may be a cellulose acetate lacquer formed in ace rdance with the following:

Percent by weight Cellulose acetate s 5 Acetone 40 Methyl Cellosolve 30 Ethyl acetate 25 solvent characteristics of the liquid, that is, they should be such as not to dissolve in the liquid.

In forming the composition, it has been found that approximately 200 ccs. of a desired liquid suspension which may be any one of those set forth above plus 10 grams of dry powdered glass beads of the type and size set forth above, produce a very efficient surface coating.

It is desirable, when forming the composition, that after the glass beads have been substantially uniformly dispersed throughout the liquid, the said composition should be allowed to settle for approximately one hour whereby the large particles will settle leaving only the fine particles in suspension. After such settling, the solution having the fine particles therein is poured off and it is then ready for use.

The above is applied to the surface of the article to be coated as by spraying, painting, dipping or other suitable method wherein a substantially uniform layer of closely related beads will remain. When said liquid dries, it forms a relatively thin coating over the beads, partially fills in the spaces between said beads and firmly bonds the beads to the face of the article as is more clearly illustrated in Fig. 3.

The above is particularly adaptable for use with the face of the so-called dark field television tubes.

If it is desired to introduce UV absorptive characteristics in said coating, an ultra-violet absorbing agent such as phenyl salicylate, quinine, piperine or other similar material soluble in the lacquer may be used. This is preferably added to the composition before the transparent particles are added thereto.

If it is desired to form a coating composition more suitable for use with a white face television tube and, in

addition to the light diffusing and UV absorbing characteristics set forth above, it is desired to introduce visible light-absorbing characteristics, this may be accomplished by either adding a suitable dye such as nigrosine or other dark or black dye to the liquid binder. For example, lamp black, colloidal carbon, Erie black or any other suitable material may be used to introduce a clear substantially neutral color and desired visible light absorption.

The UV absorbing and visible light-absorbing ingredients are preferably added to the composition before the beads are added in said solution.

Although a formula for a liquid binder which has been found to produce desirable results has been specifically set forth above and other lacquers or binders have been mentioned, it is to be understood that the liquid binder could be any suitable glue, gelatin solution, monomeric methyl methacrylate or other polymerizable liquids.

It is also to be understood that in addition to or instead of adding visible light-absorbing ingredients in the liquid suspension, glass beads having the desired lightabsorbing characteristics might be used, for example, glass having a substantially neutral clear color or other colors, with or without UV absorbing ingredients therein such as cerium or vanadium, might be used.

ltis particularly pointed out, as shown in Figs. 1 and 3, that after the coating has been applied to the surface 5 of the article 4 and the liquid binder is allowed to dry, that the said liquid forms a thin outer coating over the glass beads 11, and also forms valley-like areas 12 between said beads and further forms binder means 13 for securing the beads on the surface 5.

The function of the coating, as diagrammatically illustrated in Fig. l, is to cause the light rays, diagrammatically illustrated as coming from a source of origin 7 and which impinge upon said coating to be reflected and dispersed in a plurality of different directions as indicated by the various arrows 13 whereby no specular image of the source of origin ,7 will be visible to the eye 9 of the observer.

While the above-mentioned coating functions to diffuse and destroy the image formation of reflected light, the reflection itself may be further greatly reduced by applying to said beaded coating a non-reflecting coating such as diagrammatically illustrated at 14, see Fig. 3. Such a coating may be any one of the well known types such as is produced by evaporation of magnesium fluoride, calcium fluoride, sodium fluoride or sodium aluminum fluoride on the surface.

One of the preferred reflection-reduction coatings, how ever, if formed of a composition consisting of a colloidal suspension containing from about 0.1 to 6.0% by weight of submicroscopic, micro-granular, discrete particles of solid anhydrous transparent material such as silica, magnesium fluoride, lithium fluoride, strontium fluoride, calcium fluoride, barium fluoride or cryolitc substantially uniformly dispersed in a volatile liquid inert to the particles and the binder with the particles being approximately spherical in shape and substantially less than onequarter of the wave length of light in diameter. The beadcoated surface can be provided with the reflection-reduction coating by applying to the surface a thin layer of the above composition and causing it to dry leaving a dry coating of very minute ultra-microscopic particles on the surface, as illustrated by the numeral 14. It is desirable to control the amount of the composition applied, and also to control the concentration of the particles in the suspension to produce a reflection-reduction coating having a resultant thickness of approximately onequarter wave length of light.

The reflection-reduction coating thus formed will comprise sub-microscopic, discrete, micro-granular, transparent solid particles which are so deposited on the beaded coating as to form minute projecting irregularities on said surface, the concentration of the particles in the irregularities decreasing from the surface of the beaded coating outwardly and the material of the particles being such that the effective index of refraction of the reflectionreduction coating varies from substantially unity at the layer-air interface to an index value which progressively increases as it approaches the outer surface of the beaded coating wherein it substantially approximates the index of refraction of said beaded coating.

In order to render the above coating more resistant to abrasion, a small amount of tetraethylorthosilicate may be incorporated in the colloidal sub-microscopic suspenslon.

In Fig. 2, there is illustrated a surface similar to that illustrated in Figs. 1 and 3 with the exception that a plu rality of beaded coatings are placed in superimposed relation with each other. The coatings otherwise function in a manner similar to the beaded coating of Fig. l.

Said multiple beaded coating of Fig. 2 may be provided with a reflection-reduction coating such as illustrated diagrammatically at 14 in Fig. 3 and may be formed in any manner such as specified above.

In Fig. 4, there is diagrammatically illustrated the effect which would be obtained if the beaded coating were of the type having light-absorptive characteristics and the coating controlled as to its thickness so as to permit substantially only partial transmission therethrough, say for example, sixty per cent transmission. With this condition, the entrant ray 15, upon reaching a particle 16 of the phosphor coating 6, would cause said particle to be only sixty per cent as bright as it would be if illuminated directly by the entrant ray 15. The light reflected from the particle of phosphor 16, as illustrated by the arrow 17, upon passing through the face of the tube and through the beaded coating, will again be reduced in proportion to its first reduction when first passing through said coating and the face of the tube and will, therefore, be only thirty-six per cent of the original light of the entrant ray 15.

An additional function of the above beaded coating is illustrated in Fig. 5. In this instance, we are taking into account the illumination of the particle 16 of the phosphor coating 6 as excited by the electron stream of the conventional television tube. The light from the fluorescing particle will be only sixty per cent of its inherent value after it has passed directly through the face of the tube and the beaded coating as illustrated by the line 19. The light leaving the fluorescent particle 16 at an angle within the critical angle to the face of the tube, as indicated by the line 20, upon reaching the outer surface of the face of the tube 4 will be partially reflected rearwardly and will cause another particle 16 to be illuminated. A succession of said particles such as 16" will be similarly illuminated by reflected light. The light rays emanating from the original source 16 which are not reflected by the front face of the tube 4 will pass through the beaded coating,'as illustrated by the dash line 21, and will be reduced partially by the reflected portion thereof and by the absorption of the beaded coating whereby it will appear less than sixty per cent as bright as from the original source 16. Light at a greater angle than the critical angle, and without the beaded coating on the face of the tube, will be totally reflected and will illuminate the phosphor as, for example, at 16", but with the beaded coating thereon, the light rays will have to .pass through the beaded coating two or more times as often as the direct rays 19 and 21 and will, therefore, be greatly reduced in intensity. With the reflection-reduction coating 14 thereon, as specified above, less light will be refiectedand, therefore, less intensity of illumination at other locations, such as at 16 and 16". It will be seen, therefore, that stray light will be greatly absorbed and reduced by the beaded and reflection-reduction coatings and will be much less visible to the observer.

If it is desired to increase the diffusion characteristics of the beaded coating, this may be brought about by increasing the difference in indices of refraction of the particles and the dry suspension media as this will introduce interior diifusion effects in addition to surface diffusion. It has been found that a good difference of indices of refraction is a few units in the second decimal place of the respective indices, for example, let us assume that the index of refraction of the suspension is approximately 1.53 the particles which would work best would have an index of refraction of from 1.50 to 1.56.

While it has been specified that nigrosine or some other suitable visible light-absorbing means may be introduced in the beaded coating, it is to be understood that a visible light-absorptive dye of any suitable color or colors may be used depending upon the characteristics desired of the resultant coating and the particular pot tion of the visible spectrum which is to be reduced through absorption. This effect may be introduced either by adding such dye ingredients to the suspension liquid of the composition or by adding the desired coloring and absorptive ingredients to the glass composition from which the beads are formed. This would be particularly adaptable to television in natural colors as the color controls could be introduced by this method.

From the foregoing description, it will be seen that simple, etficient and economical means and methods have been provided for accomplishing all of the objects and advantages of the invention.

Having described my invention, 1 claim:

1. A television tube having a phosphor coating on the internal surface of the face portion thereof and having on the outer surface thereof a coating embodying a plurality of contiguously related beads of transparent material secured to said outer surface by a transparent bonding agent, said beads being approximately spherical and from 3 to 5 microns in size, and said outer coating having the beads therein having controlled absorption as to the visible portion of the spectrum.

2. A television tube having a phosphor coating on the internal surface of the face portion thereof and having on the outer surface thereof a coating embodying a plurality of contiguously related beads of transparent material adhesively secured to said outer surface and to each other by a transparent bonding agent, said particles being approximately spherical and from about 100 microns to about a wave length of the incident light in diameter, and said outer coating having the beads therein having controlled absorption as to the visible portion of the spectrum and further having controlled ultra-violet absorption.

3. The tube face of a cathode ray tube comprising a transparent member having a phosphor coating on one side thereof and having a layer of contiguously related beads of transparent material adhesively secured to the opposed side surface thereof by a thin coating of transparent bonding material surrounding the individual beads and partially filling in the spaces therebetween, said beads individually having a diameter between a dimension equal to about a wave length of the incident light and approximately 100 microns, and said beads breaking up the specular image of external light normally reflected by said surface of the member While substantially unaffecting the viewing through the transparent member of the image formed by excitation of the phosphor coating on its first-mentioned side.

4. The tube face of a cathode ray tube as claimed in claim 3 having a thin transparent reflection-reducing coating over the exposed side of said layer of contiguously related beads.

5. The tube face of a cathode ray tube as claimed in claim 3 having a transparent reflection-reducing coating over the exposed side of said layer of contiguously related beads, said transparent reflection-reducing coating comprising a plurality of submicroscopic, discrete microgranular transparent solid particles piled on the surface of said beads in the form of minute irregularities projecting to a height of a fractional wave length of the incident light and with the effective index of said layer varying from substantially unity at its air interface to an index value which progressively increases as it approaches the surface of said beads where it substantially approximates the index of refraction of the particles in massive form, said coating functioning to reduce the reflection of the light diffused and increase the transmission of the image through the transparent member and beads on its surface.

6. The face portion of a cathode ray tube comprising a transparent member having a phosphor coating on one side thereof and having a layer of contiguously related beads of transparent material adhesively secured to the opposed side surface thereof by a thin coating of transparent bonding material surrounding the individual beads and partially filling in the spaces therebetween, said beads individually having a diameter of from 3 to 5 microns for breaking up specular images of external light normally reflected by said surface of the member while substantially unaffecting viewing through said member of an image formed by excitation of said phosphor coating on its first-mentioned side.

7. A television tube having a phosphor coating on the internal surface of the face portion thereof and having on the outer surface thereof a coating embodying a plurality of contiguously related beads of transparent material adhesively secured to said outer surface by a transparent bonding agent, said beads individually being approximately spherical in shape and having a diameter more than a wave length of the light normally reflected by said outer surface and less than microns so as to diffuse the image of said reflected light without the beads being readily discernible at distances greater than ten inches.

8. A television tube as claimed in claim 7 having a thin transparent reflection-reducing coating over the exposed side of the coating of contiguously related beads.

9. A television tube as claimed in claim 7 having a thin transparent reflection-reducing coating over the exposed side of the coating of contiguously related beads, said reflection-reducing coating comprising a plurality of submicroscopic, discrete microgranular transparent solid particles piled on the surface of said beads in the form of minute irregularities projecting to a height of a fractional wave length of the incident light and with the effective index of said layer varying from substantially unity at its air interface to an index value which progressively increases as it approaches the surface of said beads where it substantially approximates the index of refraction of the particles in massive form, said coating functioning to reduce the reflection of the light diffused and increase the transmission of the image through the transparent member and beads on its surface.

References Cited in the file of this patent UNITED STATES PATENTS Re. 22,076 Cartwright et al. Apr. 21, 1942 1,176,746 Federico Mar. 28, 1916 1,491,830 Troeger Apr. 29, 1924 2,023,558 Tallman Dec. 10, 1935 2,090,922 Von Ardenne Aug. 24, 1937 2,091,152 Malpica Aug. 24, 1937 2,137,118 Schleede et al. Nov. 15, 1938 2,169,838 Herbst Aug. 15, 1939 2,197,625 Teves et al. Apr. 16, 1940 2,201,245 Ruska et al. May 21, 1940 2,222,414 Kudar Nov. 19, 1940 2,242,567 Bodde May 20, 1941 2,289,978 Malter July 14, 1942 2,293,529 Bedford Aug. 18, 1942 2,294,930 Palmquist Sept. 8, 1942 2,312,206 Calbick Feb. 23, 1943 2,346,810 Young Apr. 18, 1944 2,386,626 Nadeau et al. Oct. 9, 1945 (Other references on following page) UNITED. STATES PATENTS.

Zinde1, Jr. Oct. 30, 1945 Palmquist et a1. Sept. 27, 1946 Steadman Apr. 15, 1947 Moulton Dec. 9, 1947 Wolfson Mar. 2, 1948 Aronstein Feb. 8, 1949 8 Smith June 21, 1949 Moulton June 21, 1949 Burroughs Oct. 25, 1949 Moulton Nov. 28, 1950 Moulton Jan. 2, 1951 Heltzer Nov. 13, 1951 Barnes June 10, 1952 Szegho et a1. Sept. 30, 1952 

